先添加一个控制器

private func addChildViewController(vc:UIViewController,title:String, imageName:String ) {

        let vc = HomeTableViewController()

        vc.title = title

        vc.tabBarItem.image = UIImage(named: imageName)

        let nav = UINavigationController(rootViewController: vc)

        addChildViewController(nav)

    }

然后在一个控制器中先添加四个按钮

private func addChildViewControllers() {

        tabBar.tintColor = UIColor.orangeColor()

        addChildViewController(HomeTableViewController(), title: "首页", imageName: "tabbar_home")

        addChildViewController(MessageTableViewController(), title: "消息", imageName: "tabbar_message_center")

        addChildViewController (UIViewController())

        addChildViewController(DiscoverTableViewController(), title: "发现", imageName: "tabbar_discover")

        addChildViewController(ProfileTableViewController(), title: "我", imageName: "tabbar_profile")

}

private func addComposedButton(){

        tabBar.addSubview(composedButton)

        let count = childViewControllers.count

        let w = tabBar.bounds.width / CGFloat(count)

        composedButton.frame = CGRectInset(tabBar.bounds, 2 * w, 0)

    }